The present invention relates to gas turbine engines having convergent/divergent nozzles, and more particularly to a nozzle which provides an increased area ratio range (exit area/jet area).
A variable area exhaust nozzle optimizes the thrust produced within a gas turbine engine. In augmented gas turbine engines, convergent/divergent (C/D) nozzles provide a multitude of nozzle positions. The term “convergent-divergent” describes an exhaust nozzle having a convergent section upstream of a divergent section. Exhaust gases exiting the turbine(s) pass through the decreasing diameter convergent section before passing through the increasing diameter divergent section.
The convergent section is pivotally connected to the exhaust duct and to the divergent section. The divergent section is pivotally connected to the convergent section and to an external fairing positioned radially outboard of the divergent section. The opposite end of the external fairing is pivotally attached to a static outer case which surrounds a portion of the nozzle.
The variable orifice of the C/D nozzle is typically disposed at an interface between the aft end of the convergent section and the forward end of the divergent section. Orifice area increases and decreases when the aft end of the convergent section is displaced radially outward and inward, respectively.
The nozzle defines a throat or jet area and an exit area. The jet area is the area at which the minimum cross sectional area of the nozzle is defined. The exit area is the aft most section of the nozzle. The area ratio of a nozzle is the exit area divided by the jet area. The area ratio range provides a general indicator of engine performance and an increase in the area ratio range results in more efficient engine performance with increased engine thrust, fuel efficiency and a decrease in actuator loads required to articulate the nozzle.
The convergent and divergent sections generally include flaps and flap seals circumferentially disposed, attached to one of the other sections or to a structural member within the engine. The alternately disposed flaps and flap seals accommodate changes in orifice area and nozzle axis skew (if the nozzle is vectorable) by sliding relative to and overlapping each other as the orifice area decreases or increases.
The ability of a C/D orifice nozzle to change orifice area requires considerable flexibility in each section of the nozzle. Flexibility is provided by the flaps and flap seals overlapping one another and sliding relative to one another during nozzle geometry changes. Disadvantageously, the interfaces between flaps and/or between flaps and flap seals which permit the necessary flexibility may also restrict the area ratio range. An increase in the nozzle exit area at a high mode area ratio typically compromises the low-mode area ratio schedule due to the complexity of the flap and flap seal interface geometry.
Accordingly, it is desirable to provide a C/D exhaust nozzle with an increased high-mode area ratio schedule without compromising the low-mode area ratio schedule.